Add an ability to use the certain black list to query only domain names

[zentavr]

There are a certain black list which contain only the domains, but not IPs. I.E.: dbl.spamhaus.org. From DBL FAQ they mention:

• The Spamhaus DBL is a list of domain names with poor reputations. It is published in a domain DNSBL format. These domain reputations are calculated from many factors, and maintained in a database which in turn feeds the DBL zone itself.
• It ONLY lists domains. No IP addresses are listed by the DBL.
• The DBL is a domain-only blocklist and does not include or support IP addresses.
• An IP query against the DBL always returns a positive (listed) return code

It would be great to have a separate list file which would be used only for these kind of checks

[till]

Hadn't heard of this. Will read up on this later.